The present invention relates to an audio amplifying system and related method, and more particularly to an audio amplifying system having an improved glitch performance, and a method thereof.
In an audio system, a speaker is coupled to an audio amplifier to broadcast an audio signal generated by the audio amplifier as shown in FIG. 1. FIG. 1 is a diagram illustrating a conventional audio system 10. The conventional audio system 10 comprises an amplifier 11, a capacitor 12, a power-off detecting module 13, and a speaker 14. The amplifier 11 is operable between a supply voltage Vdd and a ground voltage Vgnd, and the amplifier 11 amplifies an input signal Vin to output an output signal Vout. The capacitor 12 is coupled between the amplifier 11 and the speaker 14 for filtering the DC level of the output signal Vout and outputting an output AC signal Vac to the speaker 14. In addition, the power-off detecting module 13 is coupled to a terminal N1, which is the terminal between the capacitor 12 and the speaker 14, for clamping the voltage level at the terminal N1 to the ground voltage Vgnd when the supply voltage Vdd is turned off to eliminate the pop-noise generated at an output terminal N2 of the amplifier 11. The power-off detecting module 13 comprises a power-off detector 13a and a bipolar junction transistor 13b. The power-off detector 13a turns on the bipolar junction transistor 13b to clamp the voltage level at the terminal N1 to the ground voltage Vgnd when it detects that the supply voltage Vdd drops to a specific voltage level.
In addition, the voltage level at the output terminal N2 of the amplifier 11 always has a close relationship with the voltage level of the supply voltage Vdd. For example, if the voltage level of the supply voltage Vdd drops sharply, the voltage level at the output terminal N2 drops sharply too. Then, when the voltage level at the output terminal N2 of the amplifier 11 drops to the ground voltage Vgnd too sharply, and the power-off detector 13a is too late to turn on the power-off detector 13a to clamp the voltage level at the terminal N1 to the ground voltage Vgnd, a glitch signal is generated at the terminal N1. The glitch signal is amplified and outputted as the pop-noise. Therefore, providing a more efficient way to eliminate the pop-noise generated by an amplifier is a significant concern in an audio system.